Newly released data from the 1997 North
American test flight of BOOMERanG, which mapped anisotropies in the cosmic
microwave background radiation (CMB) in a narrow strip of sky, show a
pronounced peak in the CMB "power spectrum" at an angular scale
of about one degree -- strong evidence that the universe is flat.

Analyzed at the Department of Energy's National Energy Research
Scientific Computing Center (NERSC) at Lawrence Berkeley National
Laboratory, the new data also suggest the existence of a cosmological
constant -- a form of countergravitational "dark energy" thought
to fill the universe.

THE POWER SPECTRUM FROM THE BOOMERANG NORTH AMERICAN TEST
FLIGHT, PLOTTED AGAINST VARIOUS MODELS OF THE UNIVERSE. THE SOLID
LINE REPRESENTS A FLAT UNIVERSE INCORPORATING A SIGNIFICANT
COSMOLOGICAL CONSTANT. OTHER CURVES REPRESENT OPEN AND CLOSED
UNIVERSES WITH DIFFERING DENSITIES OF MASS AND ENERGY.

BOOMERanG stands for "balloon observations of millimetric
extragalactic radiation and geophysics." The collaboration includes
over two dozen researchers from seven countries; its principal
investigators are Andrew Lange of the California Institute of Technology
and Paolo de Bernardis of the University of Rome, "La Sapienza."

Phillip Mauskopf of the University of Massachusetts is first author of
a letter to Astrophysical Journal Letters announcing the measurement of
the power-spectrum peak. In a second article, the BOOMERanG collaboration
presents new, independent limits on the magnitude of any cosmological
constant, a property of space that offsets gravitational attraction. Both
papers are available on the web at http://www.physics.ucsb.edu/~boomerang/papers.html.

Albert Einstein proposed the cosmological constant in 1917 but later
retracted the idea. It was dramatically resurrected in 1998 when the
international Supernova Cosmology Project based at Berkeley Lab, along
with the High-Z Supernova Search Team centered in Australia, discovered
that the expansion of the universe is not slowing down as it would be if
gravity were not offset, but instead is speeding up.

The BOOMERanG data were acquired in August, 1997, during a six-hour
flight from National Aeronautics and Space Administration's National
Scientific Balloon Facility in Palestine, Texas. The data were analyzed by
NERSC's Julian Borrill, who worked closely with colleagues at the National
Science Foundation's Center for Particle Astrophysics, located at the
University of California at Berkeley, and at the Canadian Institute of
Theoretical Astrophysics at the University of Toronto.

Borrill notes that the BOOMERanG North America data set was so large --
a partial map of the sky covering more than 200 square degrees and
containing some 26,000 pixels -- that a one-gigahertz serial processor
would have required three months of continuous operation to extract the
power spectrum, which is a measure of the structure of CMB anisotropies.

By employing the parallel processing power of the Cray T3E
supercomputer and using the MADCAP software package he developed at NERSC,
Borrill was able to shorten the running time to a matter of hours. MADCAP
-- the "microwave anisotropy dataset computational analysis
package" -- is publicly available on the web at http://cfpa.berkeley.edu/~borrill/cmb/madcap.html.

Big as it is, Borrill says, the BOOMERanG North America data is only
the first in a parade of data sets "of unprecedented quality and
ever-increasing size." The MAXIMA 1 and MAXIMA 2 balloon flights have
already produced substantially more data; their analysis is not complete.

Late last year BOOMERanG LDB (for "long duration ballooning")
completely circled the South Pole in ten and a half days, yielding a map
of virtually the whole sky visible from the pole and a data set, whose
analysis is still underway, that is more than 17 times as large as the
test flight's. Satellites to be launched early next century will produce
more data by orders of magnitude; the European Space Agency's PLANCK will
map the sky in 10,000,000 pixels.

"The memory required to process these CMB experiments increases as
the square of the number of pixels, and the time increases as the
cube," Borrill says. "Without new computers and new
computational strategies, we won't be able to derive the detailed
measurements of basic cosmological parameters the CMB experiments are
designed to reveal."

Borrill adds that "because of the power of our parallel machines
and the depth of our experience with cosmic microwave background studies,
NERSC is becoming the computing center of choice for analyzing CMB data
from experiments all over the world. We want to maintain that status, but
it will take hard work and fresh ideas."